Chapter A General rules of electrical installation design

M - Harmonic management
3 General
Fig. M3 : Installation supplying a non-linear load, where only the phenomena concerning the
50 Hz frequency (fundamental frequency) are shown
Schneider Electric - Electrical installation guide 2008
Z h
Z l
I 50 Hz
Non-linear
load
Fig. M4 : Same installation, where only the phenomena concerning the frequency of harmonic
order h are shown
V h
I h
Non-linear
load
V h = Harmonic voltage
= Z h x I h
Supply of the non-linear load creates the flow of a current I 50Hz (shown in
figure M3), to which is added each of the harmonic currents Ih (shown in figure M4),
corresponding to each harmonic order h.
Still considering that the loads reinject harmonic current upstream into the
distribution network, it is possible to create a diagram showing the harmonic currents
in the network (see Fig. M ).
Backup power
supply
G
Power-factor
correction
MV/LV
Harmonic
disturbances to
distribution network
and other users
A
Ih a
Ih b
Ih d
Ih e
(do not create
harmonics)
Rectifier
Arc furnace
Welding machine
Variable-speed drive
Fluorescent or
discharge lamps
Devices drawing rectified
current (televisions,
computer hardware, etc.)
Linear loads
Note in the diagram that though certain loads create harmonic currents in the distribution
network, other loads can absorb the harmonic currents.
Fig. M5 : Flow of harmonic currents in a distribution network
Harmonics have major economic effects in installations:
b Increases in energy costs
b Premature ageing of equipment
b Production losses
M
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